The invention relates to a condenser device for lighting an original as used in a facsimile or copying machine, and in particular, to such device which incorporates an elliptical or similar reflecting mirror for focussing light from a light source onto the surface of the original at a given slitwise zone.
It is known that the efficiency of the condenser device of the kind described, namely, the amount of light available on the original relative to the total radiation from the light source, is considerably low even though it is improved over the use of a simple condenser lens. It is evident that an elliptical reflecting mirror having a high aperture angle is effective to improve the efficiency, but the use of such a mirror results in an increased cost and may frequently be inhibited because of the space limitation. Furthermore, where a so-called cold mirror is required for preventing a severe high temperature at a light concentrated area on a target glass plate as in a facsimile system in which the target plate and condenser device are stationary and an original to be scanned runs on the target plate, one having such a high aperture angle is unavailable in fact.
On the other hand, diffuse light which is not concentrated on a given focussing area may have adverse influences on the various parts of the machine or their operation. By way of example, in a facsimile system, such diffuse light may introduce noises into an electrical signal which is to be formed from the reflective light from the original. Thus, the condenser device must be provided with a light shield.